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@@ -44,37 +44,57 @@ with this version 10+ years from now. Regression tests are here to ensure this i
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For a more detailed explanation of the algorithms, please refer to the [codecs specification PDF](documentation/codecs.pdf).
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:one:**RS01** creates error correction files which are stored separately from the image they belong to.
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:arrow_forward:**RS01** creates error correction files which are stored separately from the image they belong to.
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The artefact is an **ecc** file, which must be stored on another media than the one we're protecting.
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:two:**RS02** creates error correction data which is added to the medium to protect, we call this *augmenting* the image we're protecting.
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:arrow_forward:**RS02** creates error correction data which is added to the medium to protect, we call this *augmenting* the image we're protecting.
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Damaged sectors in the error correction information reduce the data recovering capacity,
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but do not make recovery impossible - a second medium for keeping or protecting the error correction information is not required.
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Intelligent adaptive reading is also available when reading a damaged RS02-protected disc: dvdisaster will only attempt
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to read the minimum amount of required sectors to be able to rebuild the image, using a so-called "divide and conquer"
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seeking mechanism, cutting off up to 90% of the time required to read and recover a damaged media.
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:three:**RS03** is a further development of RS01 and RS02. It can create both error correction files and
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:arrow_forward:**RS03** is a further development of RS01 and RS02. It can create both error correction files and
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augmented images, with the following added features:
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- RS03 can use multiple CPU cores and is therefore **much** faster than RS01/RS02 on modern hardware.
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- RS03 error correction files are - contrary to RS01, and to a lesser extent RS02 - robust against damage.
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- RS03 is more robust, but also more restrictive: The augmented image must completely fill the medium now while the size of augmented images can be freely chosen in RS02.
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The changes for parallel computation and higher robustness make RS03 a bit less space efficient,
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e.g. RS03 error correction data has slighly less (around -3%) error correction capacity than its RS01/RS02 counterparts on images with equal size.
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- It can use multiple CPU cores and is therefore **WAY** faster than RS01/RS02 on modern hardware.
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- RS03 augmented images and error correction files are - contrary to RS01, and to a lesser extent RS02 - robust against
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damage of the dvdisaster-added recovery data itself
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There are, however, a few cons that must be noted:
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- In image mode, the RS03 augmented image file size will be picked up from a predefined list of well-known medium sizes,
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while the size of augmented images can be freely chosen in RS02. This is the "price to pay" for the added robustness
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of the correction data.
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- In image mode, intelligent adaptive reading is not available for RS03-protected images. The "divide and conquer"
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algorithm will still be used, but dvdisaster will not stop as soon as enough sectors have been recovered to rebuild
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the image: it'll attempt to read them all until you stop it, or until it tried to read all the sectors. You can still
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stop it manually and attempt a "verify" of the resulting image file, to see if enough data has been read for recovery,
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otherwise resuming the adaptive reading until this is the case.
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- The changes for parallel computation and higher robustness make RS03 a tiny bit less space efficient, e.g. RS03 error
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correction data has slighly less (around -3%) error correction capacity than its RS01/RS02 counterparts on images with
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equal size. This is usually considered a cheap price to pay for the added robustness against corruption.
:one: Robustness against corruption of the dvdisaster-added ECC parts themselves. The higher the ranking, the less it is likely than a few badly located damaged sectors render the whole correction impossible because they affect dvdisaster metadata on-disc. For example corruption of the first dozens of sectors of an image can make RS02 entirely unusable regardless of the redundancy.
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\*Robustness against corruption of the dvdisaster-added ECC parts themselves
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:two: When algorithm is CPU-bound, i.e. generating or repairing an image stored on a SSD/NVMe drive.
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A rough decision chart follows:
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:three: Using adaptive reading when supported (RS02), linear reading otherwise (RS03), assuming a badly damaged media, taking into account the time the drive takes to try to read damaged sectors.
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